Communications system, a HVAC system employing the same and a method of manufacturing a component for the HVAC system

ABSTRACT

A communications network, a HVAC system employing a communications system and a method of manufacturing a component for the HVAC system are disclosed. In one embodiment, the communications network includes: (1) a dominant node having a predetermined coupling impedance and (2) a plurality of end nodes coupled to the dominant node, each of the plurality having an end node coupling impedance, wherein a total of each the end node coupling impedance and the predetermined coupling impedance is substantially a defined maximum loading impedance for the communication network.

TECHNICAL FIELD

This application is directed, in general, to communications networksand, more specifically, to a type of communications network employablewith Heating, Ventilating and Air Conditioning (HVAC) systems.

BACKGROUND

A concern with networks is preserving the quality of signals transmittedbetween the various components connected thereto. One way to preservesignal quality is to match impedance at the source of a signal on thenetwork and at the destination of the signal on the network. Impedancematching, however, can be difficult in multi-node networks having adistributed architecture connecting multiple components.

Communications networks for HVAC systems provide an example of suchnetworks that connect multiple components together and providecommunication paths between the multiple components for the exchange ofdata. In addition to the difficulty of a multi-node network, theconfiguration of communications networks for HVAC systems can greatlyvary depending on the installations. As such, the distances and thetopology of connection between the various components connected to thecommunications network can vary between installations. Therefore,impedance associated with the interconnections of the communicationsnetwork can also vary between different installations of the same typeof HVAC system. Furthermore, the interconnections used in HVACcommunications networks, (e.g., copper wire) may not be manufactured ata high standard for impedance matching. Accordingly, the impedancecharacteristics of a communications network itself may vary even ifinterconnecting distances and the topology are the same. To compensatefor these impedance differences, manual adjustments may be needed in thefield. For example, service or installation technicians may have toadjust dual in-line package (DIP) switches on the different componentsat the various nodes of the communications network. This may result inerrors when transmitting data via the communications network. Thus,maintaining signal quality on these types of communications networks,such as those of HVAC systems, can be a challenge.

SUMMARY

One aspect provides a communications network. In one embodiment, thecommunications network includes: (1) a dominant node having apredetermined coupling impedance and (2) a plurality of end nodescoupled to the dominant node, each of the plurality having an end nodecoupling impedance, wherein a total of each the end node couplingimpedance and the predetermined coupling impedance is substantially adefined maximum loading impedance for the communication network.

In another aspect, the disclosure provides an HVAC system. In oneembodiment, the HVAC system includes: (1) an air handler configured tocondition and circulate air for the HVAC system and (2) an air handlercontroller for the HVAC system configured to control operation of theair handler, the air handler controller including interface circuitryhaving a predetermined coupling impedance and configured to couple theair handler controller to components of the HVAC system via acommunications network of the HVAC system, wherein a total of thepredetermined coupling impedance and an end node coupling impedance ateach of the components is substantially a defined maximum loadingimpedance for the communications network.

In yet another embodiment, the disclosure provides a method ofmanufacturing a component for a HVAC system. In one embodiment, themethod includes: (1) obtaining an end node coupling impedance for acomponent of the HVAC system and (2) providing the component having theend node coupling impedance.

BRIEF DESCRIPTION

Reference is now made to the following descriptions taken in conjunctionwith the accompanying drawings, in which:

FIG. 1 illustrates a network topology diagram of an embodiment of aparallel impedance matching (PIM) network constructed according to theprinciples of the disclosure;

FIG. 2 illustrates a high-level block diagram of an embodiment of a HVACsystem constructed according to the principles of the disclosure;

FIG. 3 illustrates a high-level block diagram of an embodiment of anelectronic controller constructed according to the principles of thedisclosure;

FIG. 4 illustrates a high-level block diagram of an embodiment of a HVACcommunications network constructed according to the principles of thedisclosure; and

FIG. 5 illustrates a flow diagram of an embodiment of a method ofmanufacturing a component for an HVAC system carried out according tothe principles of the disclosure.

DETAILED DESCRIPTION

Disclosed herein is a communications network that is designed to providea universal plug and play termination scheme that preserves the qualityof signals transmitted across the network. As such, technicians do nothave to be relied on to provide matching impedances for communicationsnetworks. Instead, the disclosure provides a physical network withdesigned coupling impedances at each node of the network to preservesignal quality. Accordingly, components can be manufactured having thesedesigned (or defined) coupling impedances to provide a plug and playsolution. For example, the coupling impedances may be embedded inelectronic controllers at each node of the communications networks. Thecontrollers may be computing devices designed to direct the operation ofa particular component at each node. Interface circuitry of thecontrollers may include the coupling impedance at a node of thecommunications networks. The interface circuitry may include atransceiver of the electronic controllers and a physical interfacecircuitry for the transceiver.

In addition to providing signal stability, the disclosed network isdesigned to satisfy free network topologies. In some embodiments, theprovided communication network can have a star topology. Thecommunications network may have multiple nodes and can couple a maximumof thirty two components together. Of course, the network may be used tocouple fewer than thirty two components.

The communications length between the multiple nodes of the disclosedcommunications network can vary without affecting the signal quality. Assuch, the disclosed network can be used for HVAC systems that havevarious configurations due to installation sites. Accordingly, thedisclosed communications network can compensate for variablecommunication lengths between the coupled components. Additionally, thedisclosed communications network can compensate for different wire sizesused for interconnecting nodes of the network. As such, the providedcommunications network is wire size-agnostic.

FIG. 1 illustrates a network topology diagram of an embodiment of aparallel impedance matching (PIM) network 100 constructed according tothe principles of the disclosure. The network topology diagram providesa layout of interconnections of the various elements (e.g., nodes) ofthe PIM network 100. The PIM network 100 may be a communications networkwithin a structure. For example, the PIM network 100 may be a buildingcommunications network that is located therein and provides a medium forcommunications within the building between coupled components of thecommunications network.

The PIM network 100 includes a dominant node 110, interconnections 120and a plurality of end nodes 130. In one embodiment, the PIM network 100may be a communications network for an HVAC system. As such, thedominant node 110 and the plurality of end nodes 130 may be atcomponents of the HVAC system. Each of the nodes, the dominant node 110and each of the plurality of end nodes 130, includes a transceivercircuit having a differential input impedance. More specifically, thecircuit's differential input impedance is a combination of the circuit'stransceiver differential input impedance and the impedance of theterminating and protection elements of the circuit. In one embodiment,the dominant node 110 and the plurality of end nodes 130 may beelectronic controllers of each component at the particular nodes. Assuch, the transceiver circuit of each node may be the transceivercircuit of the electronic controllers.

The dominant node 110 is coupled to each of the plurality of end nodes130 by one of the interconnections 120 to form a physical networktopology. The interconnections 120 provide a differential communicationbus between nodes of the PIM network 100. The dominant node has usuallythe highest number of interconnections 120 connected to it. Asillustrated in FIG. 1, a length of each of the interconnections 120 mayvary. In one embodiment, the interconnections 120 may be copper wire.For example, the interconnections 120 may be 18, 20 or 22 American WireGauge (AWG) copper wire. The PIM network 100 may have a physicaltopology of a star. In one embodiment, the dominant node 100 and theplurality of end nodes 130 are coupled together in a free-topologynetwork. Free-topology network is a network where each device is tied tothe network at one point only with only a single physical path ofcommunication to any other device in the network. This thus includesstar topologies, tree topologies, bus topologies (defined in classicalsense as a continuous trunk of communication medium with two ends,having multiple short stubs attached to the trunk), but excludes ring orfully connected mesh topologies. In the PIM network 100, each of theplurality of end nodes 130 are coupled together in parallel with thedominant node 110 to form a DC (direct current) load of the network.

The dominant node 110 is established as a control node for the PIMnetwork 100 and has a predetermined coupling impedance. The dominantnode 110 circuit's differential input impedance is the predeterminedcoupling impedance for the node. Similarly, the end node 130 circuit'sdifferential input impedance is the predetermined coupling impedance forthat node, referred to as an end node coupling impedance. In oneembodiment, each of the end node coupling impedances are embedded in anelectronic controller at each of the plurality of end nodes. In someembodiments, at least one of the end node coupling impedances areembedded in an electronic controller at one of the plurality of endnodes. The predetermined coupling impedance may also be embedded in anelectronic controller at the dominant node 110. In one embodiment, thepredetermined coupling impedance has a resistance within a range of 50ohms to 200 ohms. The predetermined coupling impedance can allow variouswire sizes to be used for the interconnections 120. As such, thecommunications network 100 is a wire size-agnostic network.

The PIM network 100 has a defined maximum loading impedance. In oneembodiment, the defined maximum loading impedance is based on acharacteristic of a transceiver at the dominant node 110. Thecharacteristic may be an operating parameter of the transceiver. Thecharacteristic may be a current limit, a voltage limit, a capacitancelimit or a DC load limit for the transceiver. The transceiver may be aBosch Controller Area Network (CAN) compliant transceiver. The CANtransceiver may comply with various CAN specifications, includingrevision 2 or ISO-11898. In another embodiment, the transceiver may be aRS-485 compliant transceiver. The RS-485 transceiver may comply withvarious versions of transceivers for a RS-485 network. Thespecifications and applications notes from the manufacturers of aparticular transceiver can provide the maximum loading resistance of anetwork that the transceiver can drive. Additionally, the manufacturerinformation can also provide the differential input impedance for thetransceiver circuits of transceivers. For example, CAN transceiverTJA1050 can drive a resistive load of up to 45 Ohm, as defined by themanufacturer. As such, in some embodiments the defined maximum loadingimpedance for the PIM network 100 may be based on the characteristics ofa RS-485 compliant receiver or the characteristics of a CAN compliantreceiver.

The PIM network 100 is designed wherein a total of each of the end nodecoupling impedances and the predetermined coupling impedance, whichinclude the differential input impedances of each node's respectivetransceiver circuit, is (or substantially is) a defined maximum loadingimpedance for the communication network 100. Specific calculations arecarried out for each one of the maximum number of nodes of the PIMnetwork 100 in transmit mode and all of the remaining nodes of the PIMnetwork 100 in receive mode. The design of the PIM network 100,including the predetermined impedance and the end node couplingimpedances, is then based on the results of all of these calculations.As such, the PIM network 100 is configured to have specific impedancesbetween the coupling of the interconnections 120 at the dominant node110 and all of the couplings of the interconnections 120 at theplurality of end nodes 130. Thus, the predetermined coupling impedanceand resulting end node coupling impedances may be determined fromsimulations having multiple variables based on different type (i.e.,different gauges) of interconnections 120, different type oftransceivers at each of the nodes, operating speeds, etc. With matchingimpedances, the PIM network 100 preserves the quality of signalstraversing thereon and prohibits (or at least substantially reduces)reflections at the connections of the interconnections 120 with thedominant node 110 and the plurality of end nodes 130. The end nodecoupling impedances may be the same for each of the plurality of endnodes 130. In other embodiments, the end node coupling impedances mayvary for the different ones of the plurality of end nodes 130. As such,in some embodiments, each end node coupling impedance is substantiallythe same. In other embodiments, at least two of the end node couplingimpedances are not substantially the same.

Turning now to an example, as noted above, in one embodiment the PIMnetwork 100 is configured wherein the plurality of end nodes 130 iscoupled together in parallel with the dominant node 110. A definedmaximum loading impedance for the PIM network 100 may be determined tobe 45 ohms based on at least one characteristic of a transceiver at thedominant node 110. Through extensive simulations, the predeterminedcoupling impedance can be determined to be 50 ohms. The total impedanceof the end node coupling impedances (ENCI_(TOT)) is then 450 ohms (i.e.,45 ohms=(50 ohms×ENCI_(TOT))/(50 ohms+ENCI_(TOT))). This means that allend node impedances of the plurality of end nodes 130 which includes allminimum differential impedances (as seen from the communication lines,i.e., the interconnections 120) of each end node's respectivetransceiver circuit should not be less than 450 ohms.

In one embodiment, each end node coupling impedance may be substantiallythe same. In other embodiments, each end node coupling impedance may notbe substantially the same. Continuing with the example, the PIM network100 includes seven end nodes 130. For example, if the end node couplingimpedances are the same, and the CAN TJA1050 transceiver is used withits minimum differential input impedance of 25 kohm, then each of theplurality of end nodes 130 would have an end node coupling impedance ofapproximately 64.28571 ohms (i.e., 450 ohms divided by 7 in parallelwith 25 kohm). A terminating resistance at the end node may be adjustedand used with the differential input impedance of 25 kohms to providethe end node coupling impedance of approximately 64.28571 ohms. In thisexample, a terminating resistance of 64.4514 ohms may be used.Additionally, end node coupling impedances may not be equally divided.As such, five end nodes may have use a terminating resistance of 90.32ohms each and two end nodes use a terminating resistance of 227.04 ohmseach to reach a total of 450 ohms including the 25 kohm differentialinput impedances of the transceiver circuit.

FIG. 2 illustrates a high-level block diagram of an HVAC system 200constructed according to the principles of the disclosure. The HVACsystem 200 includes a communications network as discussed with respectto FIG. 1. As such, the HVAC system 200 includes a communicationsnetwork 260 that couples together the various components of the HVACsystem 200.

The HVAC system 200 includes an air handler 210 that is configured tocondition and circulate air for the HVAC system 200. The air handler 210may include heating and/or cooling elements to condition air and ablower to move the air through the HVAC system 200 and into anenclosure. As such, the air handler 210 may include a furnace and orevaporator coils. Additionally, the air handler 210 may be associatedwith an outdoor unit 220. Typically, the air handler 210 is an indoorunit. The outdoor unit 220 may include a compressor 222 and associatedcondenser coils 224 that are typically connected to an associatedevaporator coil in the air handler 210 by a refrigerant line 226. Oneskilled in the art will understand that the HVAC system 200 may includemultiple air handlers and, therefore, include multiple associatedcomponents as indicated in FIG. 2. Descriptions of FIG. 2, however, willonly refer to one of the components. Additionally, one skilled in theart will understand that the HVAC system 200 may include additionalcomponents, such as dampers, a thermostat, etc., that are notillustrated or discussed but are typically included in an HVAC system.

A control unit 230 controls the air handler 210 and/or the compressors222 to regulate the temperature of the premises. The display 240 canprovide additional functions such as operational, diagnostic and statusmessage displays and a visual interface that allows a technician toperform actions with respect to the HVAC system 200 more intuitively.

A comfort sensor 250 may be associated with the display 240 and may alsooptionally be associated with the control unit 230. The comfort sensor250 provides environmental data, e.g. temperature and/or humidity, tothe control unit 230. The comfort sensor 250 may be physically locatedwithin a same enclosure or housing as the control unit 230, in a manneranalogous with a conventional HVAC thermostat. In that case, the comfortsensor 250 and the control unit 230 may share the same transceivercircuit. In other embodiments, the comfort sensor 250 may be locatedseparately and physically remote from the control unit 230.

The HVAC system 200 also includes the communications network 260 that isconfigured to provide a communication medium between or among theaforementioned components of the HVAC system 200. Accordingly, thecommunications network 260 couples the air handler 210, the outdoor unit220, the control unit 230, the display 240 and the remote comfort sensor250 such that data may be communicated therebetween or thereamong. Thedata may be control data. Additionally, the communications network 260may be advantageously employed to convey one or more alarm messages orone or more diagnostic messages. Each of the components of the HVACsystem 200 includes a transceiver that is configured to communicate(transmit and receive) data over the communications network 260. Thattransceiver, together with other associated components comprises thetransceiver circuit.

The communications network 260 includes interconnections 262 and thevarious transceiver circuits 264, 265, 266, 267 and 268. Thecommunications network 260 is a PIM network as discussed with respect toFIG. 1. One of the components, or more specifically, one of thetransceiver circuits thereof, may be designated as the dominant node.For example, the transceiver circuit 264 may be designated as thedominant node. The other transceiver circuits 265, 266, 267 and 268,therefore, are end nodes.

At least some of the transceiver circuits of the communications network260 may be part of a local controller (not illustrated) for eachparticular component. Local controllers are electronic controllers thatmay be configured to provide a physical interface for the communicationsnetwork 260 and provide various functions related to networkcommunication. A representative controller for each component of theHVAC system 200 is illustrated in FIG. 3. The controller 230 may beregarded as a special case of an electronic controller, in which thecontroller 230 has additional functionality enabling it to controloperation of the various networked components, to manage aspects ofcommunication among the networked components, or to arbitrateconflicting requests for network services among these components.

FIG. 3 illustrates a high-level block diagram of an embodiment of anelectronic controller 300 constructed according to the principles of thedisclosure. The electronic controller 300 includes a transceiver circuit310, a non-volatile memory (NVM) 320, a RAM 330 and a functional block350 that may be specific to a component with which the electroniccontroller 300 is associated. The transceiver circuit 310 includesinterface circuitry 312 and a communication module 318.

The interface circuitry 312 provides an interface betweeninterconnections of a communication network (e.g., the communicationsnetwork 260 and the interconnections 262) and the remaining componentsof the electronic controller 300. The interface circuitry 312 mayinclude a physical layer interface (PLI) and a transceiver. The PLI mayinclude protection circuitry, logic circuitry, power circuitry and othercomponents or circuits to assist the transceiver in communicating overthe communications network. The PLI may include a terminating resistancethat can be adjusted to provide a desired end node coupling impedance ora predetermined coupling impedance. In some embodiments, thecommunications network may be implemented with interconnections over a4-wire cable, in which the individual conductors are assigned asfollows:

R—the “hot”—a voltage source, 24 VAC, e.g.

C—the “common”—a return to the voltage source.

i+—RSBus High connection.

-   -   i−—RSBus Low connection.

The C line may be locally grounded and a 24 VAC transformer associatedwith a component coupled to the communications network may provide powerto other components coupled thereto via the R and C lines. The 4-wirecable may be copper wire. A transceiver may include multiple connectorsfor connecting to the communications network. 4-wire interconnections,however, are not required. In other embodiments, the communicationsnetwork may be implemented with different interconnections that providea differential communication bus but is not 4-wire cable. For example,the C and R connections may not be included and 2 or 3 wireinterconnections may be used.

The communications network associated with the controller 300 may beconfigured as a star network with a furnace transceiver circuit as thedominant node. Thus, the furnace may include three separate connectorsconfigured to accept a connection to the communications network. Twoconnectors may be 4-pin connectors: one 4-pin connector may be dedicatedfor connecting to an outdoor unit, and one may be used to connect toequipment other than the outdoor unit. The third connector may be a2-pin connector configured to connect to another component or networkvia the i+/i− signals.

The communication module 318 is configured to broadcast and receivemessages over the communication network via the transceiver of theinterface circuitry 312. The functional block 350 may include one ormore of various components, including without limitation amicroprocessor, a state machine, volatile and nonvolatile memory, apower transistor, a monochrome or color display, a touch panel, abutton, a keypad and a backup battery. The electronic controller 300 maybe associated with a particular component of a system, such as the HVACsystem 200, and may provide control thereof via the functional block350. The NVM 320 provides local persistent storage of certain data, suchas various configuration parameters. The RAM 330 may provide localstorage of values that do not need to be retained when the electroniccontroller 300 is disconnected from power, such as results fromcalculations performed by control algorithms.

With respect to the PIM network 100 and the communications network 260,the controller 300 may be considered a node and include the appropriatecoupling impedance for the network. In one embodiment, the interfacecircuitry 312 of the transceiver circuit 310 may include a predeterminedcoupling impedance or an end node coupling impedance depending on theuse of the controller 300 within the network.

FIG. 4 illustrates a high-level block diagram of an embodiment of a HVACcommunications network 400 constructed according to the principles ofthe disclosure. The network 400 includes multiple nodes coupled togethervia interconnections 450. The interconnections may be copper wire. Forexample, the interconnections 450 may be a 4-wire cable as discussedabove with respect to FIG. 3. The nodes of the communications network400 may be controllers (not illustrated) of the various illustratedcomponents. The controllers may include transceiver circuits to directcommunications via the communications network 400 and provideterminations for the interconnections 450. One of the components, or acontroller thereof, may be designated a dominant node wherein theremaining components are end nodes. The components include a controller410, a user interface 420, a comfort sensor 430 and a furnace 440configured to communicate over the interconnections 450. In someembodiments these devices form a minimum HVAC network. In addition, thenetwork 400 is illustrated as connecting an outdoor unit 460, an outdoorsensor 470, and a gateway 480. The transceiver of each of thesecomponents may be coupled to the interconnections 450 to form thecommunications network 400.

The controller 410 is configured to control the furnace 440 and theoutdoor unit 460 using, such as command messages sent via theinterconnections 450. The controller 410 receives environmental data,including temperature and/or humidity, from the comfort sensor 430, thefurnace 440, the outdoor sensor 470 and the outdoor unit 460. The datamay be transmitted over the communications network 400 by way ofmessages formatted for this purpose. The user interface 420 may includea display and input means to communicate information to, and acceptinput from, an operator or manager of the network 400. The display andinput means may be a touch-sensitive display screen.

The controller 410, comfort sensor 430 and user interface 420 mayoptionally be physically located within a control unit 490. The controlunit 490 provides a convenient terminal to the operator to effectoperator control of the system 100. In this sense, the control unit issimilar to the thermostat used in conventional HVAC systems. However,the control unit 490 may only include the user interface 420, with thecontroller 410 and comfort sensor 430 remotely located from the controlunit 490.

The controller 410 may control HVAC functionality, store configurations,and assign addresses during system auto configuration. The userinterface 420 provides a communication interface to provide informationto and receive commands from a user. The comfort sensor 430 may measureone or more environmental attributes that affect user comfort, e.g.,ambient temperature, RH and pressure. The three logical devices 410,420, 430 each send and receive messages over the communications network400 to other devices attached thereto, and have their own addresses onthe network 400.

FIG. 5 illustrates a flow diagram of a method of manufacturing acomponent for an HVAC system carried out according to the principles ofthe disclosure. The component may include a controller to direct theoperation of the component. In other embodiments, the component itselfmay be a controller for the HVAC system. The controller may include atransceiver circuit for coupling the component to a communicationsnetwork of the HVAC system. The method begins in a step 505.

In a step 510, an end node coupling impedance for a component of theHVAC system is obtained. The component is intended to be coupled to acommunications network of the HVAC system. The end node couplingimpedance may be obtained based on defined maximum loading impedance forthe communications network and a predetermined coupling impedance for adominant node of the communications network. The end node couplingimpedance may be provided by a manufacturer of the HVAC system to thirdparty vendors for manufacturing the component.

In a step 520, the component is provided with the end node couplingimpedance. As such, a technician in the field does not need to be reliedon to obtain the proper impedance when servicing or replacing componentsof the HVAC system. Instead, the component can be coupled to thecommunications network to provide a plug and play scheme for the HVACsystem. The component may be provided by a manufacturer who constructsthe component with the end node coupling impedance. In one embodiment, atransceiver circuit of the component may include the end node couplingimpedance. For example, interface circuitry of the transceiver circuit,such as a PLI of the interface circuitry, may be manufactured with theend node coupling impedance. The interface circuitry is used to connectthe component to the communications network of the HVAC system. Theinterface circuitry may include terminals or other types of connectorsthat are used to terminate a conductor. The interface circuitry may beprovided during manufacturing of the component. The method 500 ends in astep 530.

Those skilled in the art to which this application relates willappreciate that other and further additions, deletions, substitutionsand modifications may be made to the described embodiments.

What is claimed is:
 1. A communication network, comprising: a dominantnode having a predetermined coupling impedance; a plurality of end nodescoupled to said dominant node, each of said plurality having an end nodecoupling impedance, wherein a total of each said end node couplingimpedance and said predetermined coupling impedance is a defined maximumloading impedance for said communication network; wherein an end nodecoupling impedance of one of said plurality of end nodes is determinedbased on said predetermined coupling impedance and end node couplingimpedances of remaining ones of said plurality of end nodes.
 2. Thecommunication network as recited in claim 1 wherein said defined maximumloading impedance is determined based on a characteristic of atransceiver at said dominant node.
 3. The communication network asrecited in claim 2 wherein said transceiver is a CAN complianttransceiver.
 4. The communication network as recited in claim 2 whereinsaid transceiver is a RS-485 compliant transceiver.
 5. The communicationnetwork as recited in claim 1 wherein said predetermined couplingimpedance has a resistance within a range of 50 ohms to 200 ohms.
 6. Thecommunication network as recited in claim 1 wherein said plurality ofend nodes is coupled to said dominant node via copper wire.
 7. Thecommunication network as recited in claim 1 wherein a maximum number ofsaid plurality of end nodes is in a range of one to thirty-one.
 8. Thecommunication network as recited in claim 1 wherein each said end nodecoupling impedance is the same.
 9. The communication network as recitedin claim 1 wherein at least two of said end node coupling impedances arenot the same.
 10. The communication network as recited in claim 1wherein communication lengths between said plurality of end nodes andsaid dominant node vary.
 11. The communication network as recited inclaim 1 wherein said dominant node and said plurality of end nodes arecoupled together in a free-topology network.
 12. The communicationnetwork as recited in claim 1 wherein said plurality of end nodes arecoupled together in parallel.
 13. The communication network as recitedin claim 1 wherein said communicating network is a buildingcommunication network.
 14. The communication network as recited in claim1 wherein said communicating network is a HVAC communications andcontrol network and said dominant node and said plurality of end nodesare HVAC components.
 15. The communication network as recited in claim 1wherein said predetermined coupling impedance is embedded in anelectronic controller.
 16. The communication network as recited in claim1 wherein at least one of said end node coupling impedances is embeddedin an electronic controller.